The present invention relates to a temperature actuated flow restrictor, also called a thermostat valve, for controlling gas flow to a heater. More particularly, this invention relates to an improved thermostat valve for controlling the flow of natural gas or propane for powering an infrared catalytic heater.
Catalytic heaters employ a catalyst bed which results in flameless combustion of the fuel and the creation of infrared energy. Since combustion is flameless, these heaters may operate at a temperature that is lower than the ignition temperature of the natural gas or propane. Catalytic heaters are thus particularly well suited for applications desiring explosion proof operation, such as various applications involving the natural gas industry. In a typical catalytic heater, a catalyst bed is heated to a temperature of about 250xc2x0 Fahrenheit at which time the thermostat valve is opened so that the supplied fuel and oxygen form the desired reaction with the catalyst bed. When a desired temperature in a room or area about the heater is achieved, the amount of gas supplied to the heater must be reduced. It is important, however, that the supply of gas flow not be completely shut-off since removing the fuel supply would allow the catalyst to cool below the reaction temperature, which would then again require the catalyst bed to be raised to above 250xc2x0 F. to restart the reaction.
Conventional thermostat valves for most natural gas or propane consuming devices are designed to close off the fuel supply at a set point temperature. When such valves are used with catalytic heaters, manufacturers have modified the valves to add an orifice through the valve body to allow a reduced gas flow to pass through the thermostat valve when closed, thereby reducing the heater output. Conventional thermostat valves are quite large and thus expensive, since these thermostat valves are generally designed for use with equipment which uses a much higher flow rate of natural gas or propane than do catalytic heaters. Conventional thermostat valves are also complex, and frequently require high maintenance and repair costs.
Various types of valves have been designed which utilize a thermally responsive disk, which is typically a bi-metal disk having two metallic layers bonded together with one of the layers having a higher thermal coefficient of expansion than the other. U.S. Pat. Nos. 3,856,259, 3,930,613, 4,076,172, and 4,142,676 disclose prior art valves with bi-metal disks. In general, these valves are also complex and utilize various schemes for enabling the snap disk to close off flow through the valve. U.S. Pat. No. 4,133,478 discloses a snap disk with a spider-type spring and an O-ring valve seat. U.S. Pat. No. 4,295,602 discloses a valve intended for use to limit the temperature of hot water in a shower system, and restricts the water flow when the snap disk is in the closed position. Since no elastomeric seal is provided for engagement with the snap disk, the flow rate of the restricted water may vary. U.S. Pat. No. 4,557,019 discloses a flow control device intended for use with a gas analyzer and a heated sampling system to prevent liquid condensation in the system. None of the above prior art patents disclose a valve which is intended to control the flow of natural gas or propane to an infrared catalytic heater.
The disadvantages of the prior art are overcome by the present invention, and an improved thermostat valve for controlling gas flow to a catalytic heater is hereinafter disclosed.
A thermostat valve according to the present invention is particularly designed for controlling the flow of gas, such as natural gas or propane, to fuel an infrared catalytic heater. In one embodiment, the valve includes a housing having a central flow path between the inlet port and the outlet port, and a snap disk movable with respect to the housing between open and closed positions. An elastomeric seal supported on the housing is intended for engagement with the snap disk when in the closed position. A restricted flow path spaced radially outward from the elastomeric seal allows a restricted quantity of gas to pass to the heater when the snap disk is closed. The snap disk may include a plurality of through ports for passing gas through the central flow path when open and through the restricted flow path in the housing when closed. An O-ring may be used as a biasing member for engaging a periphery of the snap disk to bias the snap disk for engagement with the elastomeric seal. When the heater raises the temperature to a desired level, the snap disk will move to the closed position to seal off flow through the central flow path in the valve. A reduced amount of gas continues to flow through the restricted flow path to prevent the heater from cooling below the catalyst reaction temperature. When the temperature drops below a selected value, the snap disk will move to the open position to allow flow through the central flow path in the housing, thereby providing an increased fuel flow rate to the heater to raise the surrounding temperature. In another embodiment, the snap member is provided with the restricted flow path for passing a limited quantity of gas to the heater when the snap member is closed.
It is an object of the present invention to provide a relatively low cost yet highly reliable thermostat valve for controlling gas flow to an infrared catalytic heater. A related object of the invention is to provide a thermostat valve which is simple and has few, and preferably only one, moving part.
It is a feature of the invention that the thermostat valve may be manufactured to operate at various temperatures by changing the bi-metal disk.
It is another feature of the invention that the safety of the thermostat valve is enhanced by providing a valve which does not require any user adjustments.
It is a significant advantage of the invention that the thermostat valve is simple, highly reliable, and has a relatively low manufacturing and maintenance cost.
These and other objects, features, and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.